Heat exchanger

ABSTRACT

In order to alleviate reduction in a heat exchange capability and to further improve the heat exchange capability, a heat exchanger of the present invention includes: a heat sink; and an electron emitting element which is provided so as to be separated from the heat sink by a space and which provides electrons to the heat sink via air in the space. The electron emitting element includes: an electrode substrate; a thin-film electrode; a power supply which applies a voltage between the electrode substrate and, the thin-film electrode; and an electron acceleration layer which accelerates electrons inside the electron acceleration layer in response to the voltage applied by the power supply so that the electrons are emitted from the thin-film electrode. The electron acceleration layer is made at least partially of an electric insulating material. The heat exchanger includes an air filter through which air flows onto a surface of the thin-film electrode. This can alleviate reduction in the heat exchange capability, caused by dust that adheres to a surface of the electron emitting element and therefore can attain an excellent heat exchange capability for long periods.

This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2009-256347 filed in Japan on Nov. 9, 2009, the entire contents of which are hereby incorporated by reference,

TECHNICAL FIELD

The present invention relates to a heat exchanger.

BACKGROUND ART

A heat exchanger disclosed in Patent Literature 1 is proposed as a heat exchanger that employs an electron emitting element. The heat exchanger (heating element radiator 1) includes: a heating element 2; a heat sink 3 which is in contact with the heating element 2; and an electron emitting element 4 which is provided so as to be separated from the heat sink 3 by a space and which provides electrons to the heat sink 3 via air in the space. The electron emitting element 4 includes: an electrode substrate 7; a thin-film electrode 9; a power supply 10 which applies a voltage between the electrode substrate 7 and the thin-film electrode 8; and an electron acceleration layer 8 which accelerates the electrons inside the electron acceleration layer 8 in response to the voltage applied by the power supply 10 so that the electrons are emitted from the thin-film electrode 9. The electron acceleration layer 8 is made at least partially of an electric insulating material. It is therefore possible to maintain and improve a heat exchange capability independently of a configuration in which electric field concentration tends to occur.

Patent Literature 2 discloses an arrangement in which a pretreatment process is carried out before a process of using an electron emitting element in vacuum, and the pretreatment changes an electric property of the electron emitting element by flowing a current into the electron emitting element while the electron emitting element is being exposed to methane.

Citation List

Patent Literature

Patent Literature 1

Japanese Patent No. 4314307 A (Publication Date: Aug. 12, 2009)

Patent Literature 2

Japanese Patent Application Publication Tokukai, No. 2001-195973 A (Publication Date: Jul. 19, 2001)

SUMMARY OF INVENTION Technical Problem

However, the heat exchanger disclosed in Patent Literature 1 still poses the following problem.

That is, use of an electron emitting element in the heat exchanger improves a heat exchange capability. However, the improvement of the heat exchange capability is not sufficient. Further, in a case where the electron emitting element is such an electron emitting element that a part of an electron acceleration layer between an upper electrode and a lower electrode is made of an insulator, there is such a drawback that dust in an airflow adheres to a surface of the electron emitting element, thereby causing gradual reduction in the heat exchange capability (cooling effect).

Furthermore, the heat exchange capability is also reduced by adhesion of traces of gas to the surface of the electron emitting element. The following shows, as an example, that a capability of the electron emitting element is changed or deteriorated by traces of gas. The capability of the electron emitting element is greatly changed or deteriorated in a case of insufficient vaporization of toluene or alcohol used as an organic solvent for producing the electron emitting element. Further, in a case where the produced electron emitting element is exposed to ethanol or vapor, the capability of the produced electron emitting element is also greatly changed and deteriorated. Furthermore, the electron emitting element disclosed in Patent Literature 2 is an example in which a property of the electron emitting element is changed by traces of gas though a detailed mechanism of the change of the property is unclear.

Solution to Problem

The present invention is made in view of the problem, and an object of the present invention is to attain a heat exchanger which can alleviate reduction in a heat exchange capability and which can further improve the heat exchange capability.

A heat exchanger of the present invention, in order to attain the object, including: an electron emitting element; and an air filter, the electron emitting element being provided so as to be separated, by a space, from a target of heat exchange having electrical conductivity and providing electrons to the target of heat exchange via air in the space, and the heat exchanger exchanging heat between the target of heat exchange and the air, the electron emitting element including: an electrode substrate; a thin-film electrode; first voltage applying means for applying a voltage between the electrode substrate and the thin-film electrode; and an electron acceleration layer which accelerates electrons inside the electron acceleration layer in response to the voltage applied by the first voltage applying means so that the electrons thus accelerated are emitted from the thin-film electrode, the electron acceleration layer being made at least partially of an electric insulating material, and the air filter filtering air to flow onto a surface of the electron emitting element.

The heat exchanger of the present invention (i) includes the electron emitting element which is provided so as to be separated, by a space, from the target of heat exchange having electrical conductivity and which provides the electrons to the target of heat exchange via the air in the space, and (ii) exchanges heat with the target of heat exchange. Further, the electron emitting element includes: the electrode substrate; the thin-film electrode; the first voltage applying means for applying a voltage between the electrode substrate and the thin-film electrode; and the electron acceleration layer which accelerates the electrons inside the electron acceleration layer in response to the voltage applied by the first voltage applying means so that the electrons are emitted from the thin-film electrode. The electron acceleration layer is made at least partially of an electric insulating material. This arrangement makes it possible to realize an electron emitting element which can emit electrons in an internal electric field. In other words, the electron emitting element provides electrons to the target of heat exchange via the air present in the space between the electron emitting element and the target of heat exchange. These electrons collide with and adhere to air molecules present in the space. This collision and adhesion ionize the air molecules. These air molecules thus ionized move along an electric field. This generates an ionic wind. The ionic wind brings ions thereof to the target of heat exchange. This stirs air molecules which are heated on a surface of the target of heat exchange thereby causing heat exchange between the target of heat exchange and the air present along the surface of the target of heat exchange. As a result, the target of heat exchange is cooled.

As described above, according to the above arrangement, the electron emitting element which can emit the electrons in the internal electric field is provided so as to be separated from the target of heat exchange by a space. Therefore, the electron emitting element can stably provide electrons into the atmosphere, and thus can generate an ionic wind. As a result, the electron emitting element can attain an excellent heat exchange capability.

According to the arrangement, the heat exchanger further includes the air filter through which air flows onto the surface of the thin-film electrode. It is therefore possible to prevent adhesion of dust to the surface of the electron emitting element. This can alleviate reduction in the heat exchange capability (cooling effect) caused by the duct that adheres to the surface of the electron emitting element and therefore can attain the excellent heat exchange capability (cooling effect) for long periods.

As described above, the above arrangement makes it possible to realize a heat exchanger which can alleviate reduction in the heat exchange capability and which can further improve the heat exchange capability.

For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.

Advantageous Effects of Invention

According to the present invention, the electron emitting element is configured such that the electron acceleration layer made at least partially of the electric insulating material is provided between the electrode substrate and the thin-film electrode. This can attain the excellent heat exchange capability. The heat exchanger also includes the air filter through which air flows onto the surface of the thin-film electrode. This alleviates reduction in the heat exchange capability, caused by dust that adheres to the surface of the electron emitting element and therefore attains the excellent heat exchange capability for long periods. As a result, it is possible to attain the heat exchanger which can alleviate reduction in the heat exchange capability and which can further improve the heat exchange capability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating a preferable example of a heat exchanger (cooling device) in accordance with an embodiment of the present invention.

FIG. 2 is an enlarged view illustrating main portions of a heat sink and an electron emitting element included in the heat exchanger illustrated in FIG. 1.

FIG. 3 is an enlarged cross-sectional view illustrating a main portion of an electron acceleration layer included in the heat exchanger illustrated in FIG. 1.

FIG. 4 is a cross-sectional view illustrating an arrangement of a heating element radiator used in Example 1.

FIG. 5 is a graph illustrating a result of verifying a cooling effect with use of the heating element radiator of Example 1.

FIG. 6 is a cross-sectional view illustrating an arrangement of an electron emitting element included in a heat exchanger (cooling device) in accordance with another embodiment of the present invention.

FIG. 7 is a plan view illustrating an arrangement of a rotary-blade airflow generator included in a heat exchanger (cooling device) in accordance with still another embodiment of the present invention.

FIG. 8 is a perspective view illustrating an arrangement of an electron emitting element included in a heat exchanger (cooling device) in accordance with yet another embodiment of the present invention.

FIG. 9 is a cross-sectional view illustrating a heat exchanger in accordance with further yet another embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

A heat exchanger of the present invention is a device which transfers an ionic wind to a target of heat exchange and which exchanges heat between the target of heat exchange and air present along a surface of the target of heat exchange. The following describes how the heat exchanger exchanges heat. In the heat exchanger, the ionic wind generates, the ionic wind brings ions thereof to the target of heat exchange. This stirs air molecules which are heated on the surface of the target of heat exchange thereby causing heat exchange between the target of heat exchange and the air present along the surface of the target of heat exchange.

The heat exchange encompasses: a heat exchange involving heat transfer from a target of heat exchange having a relatively high temperature to relatively low-temperature air; and a heat exchange involving heat transfer from relatively high-temperature air to a target of heat exchange having a relatively low temperature. The following embodiments describe, as an example of the heat exchanger of the present invention, a heating element radiator (cooling device) that exchanges heat so that the heat is transferred from the target of heat exchange having a relatively high temperature to relatively low-temperature air.

The “target of heat exchange” of the present invention means a target to which an electron emitting element emits electrons. The following embodiments describe a device in which a heat sink is used as the “target of heat exchange”, the heat sink is cooled by the ionic wind and thus a heating element that is directly in contact with the heat sink is indirectly cooled. That is, in the following embodiments, heat exchange occurs between the heat sink and air present along a surface of the heat sink and also occurs between the heat sink and the heating element.

The “heating element” that serves as the “target of heat exchange” may be cooled directly by the ionic wind.

First Embodiment

One embodiment of the present invention is described below with reference to FIGS. 1 through 9. Note that an arrangement described below is merely a specific example of the present invention. Thus, the present invention is not limited to this arrangement. FIG. 1 is a cross-sectional view illustrating a preferable example of a heating element radiator (cooling device) 1 according to the present embodiment.

The heating element radiator 1 is a device for releasing, to the outside, heat generated by a heating element 2. The heating element radiator 1 includes: a heat sink (target of heat exchange) 3; an electron emitting element 4; and a power supply (second voltage applying means) 5. The heat sink 3, which is made of an electrically conductive material, is in contact with the heating element 2 on one side. The heat sink 3 has a surface 3 a on the other side opposite to the side thereof where the heating element 2 is provided. The surface 3 a is in contact with air. The heat sink 3 includes a plurality of convexities 3 b that are formed on at least a part of the surface 3 a. The electron emitting element 4 is provided so as to face the surface 3 a, of the heat sink 3. The electron emitting element 4 is separated from the surface 3 a of the heat sink 3 by a space, and thus provides electrons to the heat sink 3 via the air in the space. Air flows into the space between the electron emitting element 4 and the surface 3 a of the heat sink 3 via an air filter (not shown). The heat sink 3 and the electron emitting element 4 are connected to the power supply 5. The power supply 5 thus applies a voltage between the heat sink 3 and the electron emitting element 4. This voltage causes the electron emitting element 4 to emit electrons. These electrons collide with and adhere to air molecules present along the space between the heat sink 3 and the electron emitting element 4. This collision and adhesion then ionize the air molecules. The air molecules thus ionized move along directions indicated by arrows shown in FIG. 1 (i.e., through an electric field generated between the heat sink 3 and the electron emitting element 4). This generates an ionic wind. The ionic wind brings ions thereof to the heat sink 3. This stirs and exchanges air molecules which are present along the surface of the heat sink 3 and which are heated by the heating element 2. The arrival of the ions at the heat sink 3 will cause the heat sink 3 to be charged up. In order to prevent the heat sink 3 from being charged up, the heating element radiator 1 is connected to ground 6.

FIG. 2 is an enlarged view illustrating respective main portions of the heat sink 3 and the electron emitting element 4 included in the heating element radiator 1 illustrated in FIG. 1. As illustrated in FIG. 2, the electron emitting element 4 includes: an electrode substrate 7; an electron acceleration layer 8; a thin-film electrode 9; and a power supply (first voltage applying means) 10. The electron acceleration layer 8 is sandwiched between the electrode substrate 7 and the thin-film electrode 9. The power supply 10 applies a voltage between the electrode substrate 7 and the thin-film electrode 9. The electron acceleration layer 8 is made at least partially of an electric insulating material. The electron emitting element 4 accelerates electrons between the electrode substrate 7 and the thin-film electrode 9 (i.e., in the electron acceleration layer 8) in response to the voltage applied between the electrode substrate 7 and the thin-film electrode 9. The electron emitting element 4 thus emits the electrons from the thin-film electrode 9.

As described above, the heating element radiator includes the two power supplies 5 and 10. The power supply 10 is used to accelerate electrons in the electron acceleration layer 8 of the electron emitting element 4 so that the electrons are emitted from the thin-film electrode 9. On the other hand, the power supply 5 is used to provide, to the heat sink 3, the electrons emitted from the thin-film electrode 9.

Further, the heating element radiator 1 includes: a fan 23 that serves as air supplying means which supplies an airflow to the space between the heat sink 3 and the electron emitting element 4; and an air filter 24. The air filter 24 is provided between (i) the space between the heat sink 3 and the electron emitting element 4 and (ii) the fan 24. Airflow 23 a supplied by the fan 23 flows, via the air filter 24, into the space between the heat sink 3 and the electron emitting element 4. The air filter 24 is a filter that collects and filters dust present in the airflow 23 a.

As described above, in the heating element radiator 1, the airflow 23 a flows, via the air filter 24, into the space between the heat sink 3 and the electron emitting element 4. This allows the airflow 23 a from which dust has been removed to flow onto a surface of the thin-film electrode 9. The heating element radiator 1 thus can prevent adhesion of dust to the surface of the thin-film electrode 9. Accordingly, the heating element radiator 1 can alleviate reduction in a cooling effect caused by the dust that adheres to the surface of the electron emitting element 4 and therefore can attain an excellent cooling effect for long periods.

Further, the air filter 24 may be a filter that collects and filters traces of gas in the atmosphere. The “traces of gas in the atmosphere” described in this embodiment is VOC (volatile organic compounds), ozone, vapor or the like. VOC has volatility, and is a general term of an organic compound that becomes a gas in the atmosphere. Examples of VOC include various substances such as toluene, xylene and ethyl acetate. As described above, the air filter 24 is a filter that collects and filters traces of gas present in the atmosphere. This reduces adhesion of traces of gas to the electron emitting element 4 and therefore yields an effect which prevents deterioration in a capability of the electron emitting element 4 which deterioration is caused by the adhesion of traces of gas to the electron emitting element 4. Further, in order to collect and filter traces of gas present in the atmosphere, the air filter 24 preferably includes at least one of active carbon, manganese dioxide and titanium oxide. The active carbon absorbs various traces of gas, the manganese dioxide is mainly advantageous to resolution of ozone, and the titanium oxide is advantageous to resolution of VOC.

In a case where the electron emitting element 4 is used for heat exchange in the atmosphere as in the heating element radiator 1, removal of traces of gas present in the atmosphere by use of the air filter 24 is greatly advantageous to maintaining the capability of the electron emitting element 4 for long periods.

The heat sink 3 may be separated from the thin-film electrode 9 by any distance, provided that it is possible to provide, to the heat sink 3, the electrons emitted from the thin-film electrode 9. The distance, for example, falls preferably within a range from 100 μm to 50 cm, more preferably within a range from 100 μm to 10 mm, or particularly preferably within a range from 100 μm to 1 mm.

The electrode substrate 7 of the electron emitting element 4 included in the heating element radiator 1 may be (i) a substrate made of a metal such as SUS, Ti, and Cu, or (ii) a substrate made of a semiconductor such as Si, Ge, and GaAs. Alternatively, in a case where an insulator substrate such as a glass substrate is used as the electrode substrate 7, an electrically conductive material such as a metal may be attached to the insulator substrate along an interface between the insulator substrate and the electron acceleration layer 8 so as to serve as an electrode.

The thin-film electrode 9 is used to apply a voltage into the electron acceleration layer 8. The thin-film electrode 9 may thus be made of any material, provided that the material allows the voltage application. However, the electrons accelerated through the electron acceleration layer 8 and thus having a high energy are desirably transmitted through the thin-film electrode 9 and emitted therefrom with a smallest possible energy loss. In view of this, it is preferable to use a material which has a low work function and of which a thin film can be made. This can achieve a greater effect. Examples of such a material encompass gold, carbon, titanium, nickel, tungsten and aluminum.

The electron acceleration layer 8 may be made at least partially of an electric insulating material. The electric insulating material constituting the at least part of the electron acceleration layer 8 preferably includes particulate electric insulating particles. With this arrangement, the electron emitting element 4 accelerates electrons between the electrode substrate 7 and the thin-film electrode 9 (i.e., in the electron acceleration layer 8) in response to the voltage applied between the electrode substrate 7 and the thin-film electrode 9. The electron emitting element 4 can thus emit the electrons from the thin-film electrode 9.

The following present embodiment describes an arrangement of the electron acceleration layer 8. The electron acceleration layer 8 includes: electrically conductive particles each of which is made of an electrically conductive material and which is surrounded by a first dielectric material; and a second dielectric material larger than the electrically conductive particles. In this embodiment, the first dielectric material is a coating material which coats the electrically conductive particles, and this embodiment describes the electrically conductive particles as insulatively coated metal particles 12. Further, this embodiment describes the second dielectric material as electric insulator particles 11 having an average diameter larger than an average diameter of the metal particles 12 which are insulatively coated. However, an arrangement of the electron acceleration layer 8 is not limited to this embodiment. The electron acceleration layer 8 may, for example, be arranged as follows: The electric insulating material takes the form of a sheet, and is provided on the electrode substrate 7. The electric insulating material has a plurality of openings which penetrate the electric insulating material in a direction from the electrode substrate 7 to the electric insulating material. These openings contain the electrically conductive particles which are dielectrically coated with the coating material.

FIG. 3 is an enlarged cross-sectional view illustrating a main portion of the electron acceleration layer 8 included in the heating element radiator 1. As illustrated in FIG. 3, the electron acceleration layer 8 includes: the electric insulator particles 11 which serve as the second dielectric material; and the metal particles 12 which serve as the electrically conductive particles and which are made of the electrically conductive material surrounded by the first dielectric material. The electron acceleration layer 8, as described above, includes two kinds of particles, namely the electric insulator particles 11 and the metal particles 12.

The insulatively coated metal particles 12 may be of any kind of metal, provided that an operating principle of generating ballistic electrons can be realized. However, in order to prevent oxidative degradation from occurring when the heat exchange is carried out under an atmospheric pressure, it is preferable to use a metal which is not easily oxidized. Examples of such a metal encompass gold, silver, platinum, nickel and palladium. Also, the insulating coating for the insulatively coated metal particles 12 may be any insulating coating, provided that the operating principle of generating ballistic electrons can be realized. However, if the insulating coating is formed with a coating made of oxidized metal particles, such an oxide coating may be subject to oxidative degradation in the atmosphere, and in turn may have a thickness larger than a desired thickness. Thus, in order to prevent oxidative degradation from occurring when heat exchange is carried out under the atmospheric pressure, the insulating coating is preferably made of an organic material. Examples of such an organic material encompass alcoholate, aliphatic acid and alkanethial. According to the principle (described below in detail) of generating ballistic electrons, it is important that the insulatively coated metal particles 12 each are not larger than 10 nm in diameter, and also the insulating coating is more effective when having a smaller thickness.

The electric insulator particles 11 may be made of any material, provided that the material is an electric insulating material. The electric insulator particles 11 desirably make up 80 w % to 95 w % of all materials included, in the electron acceleration layer 8. In order to achieve an appropriate resistivity and heat dissipation effect, it is arranged to include 2 to 300 metal particles 12 for every electric insulator particle 11. In other words, the electric insulator particles 11 and the metal particles 12 are present at a number ratio of 1:2-300. Further, in order to achieve an effective heat dissipation to the metal particles 12, a diameter of the electric insulator particles 11 is preferably larger than that of the metal particles 12. Specifically, the electric insulator particles 11 each preferably have a diameter (average diameter) of 10 nm to 1000 nm. Thus, the electric insulator particles 11 are practically made of a material such as SiO₂, Al₂O₃, and TiO₂.

A thinner electron acceleration layer 8 allows a stronger electric field to be applied to the thinner electron acceleration layer 8. Hence, a thin electron acceleration layer 8 only requires a low voltage to be applied thereto in order to accelerate electrons. The electron acceleration layer 8 cannot have a thickness smaller than the average diameter of the electric insulator particles 11. Thus, the electron acceleration layer 8 preferably has a thickness within a range from 5 nm to 1000 nm.

This embodiment describes an arrangement in which the metal particles 11 are each surrounded by the first dielectric material. However, the arrangement of the metal particles 11 is not limited to this embodiment. The metal particles 11 may be arranged such that the metal particles 11 are each not surrounded by the first dielectric material or that the metal particles 11 are each not coated by the first dielectric material but the first dielectric material interspersedly adheres to the metal particles 11, in the heating element radiator 1. Such arrangements also can accelerate electrons between the electrode substrate 7 and thin-film electrode 9 (that is, in the electron acceleration layer 8) so that the electrons are emitted from the thin-film electrode 9.

The electron acceleration layer 8 may be made at least partially of an electric insulating material. The electron acceleration layer 8 may not include the metal particles 12. Examples of such an arrangement of the electron acceleration layer 8 encompass: an arrangement disclosed in Japanese Patent Application Publication Tokugan No. 2009-121455 (not yet laid open to the public at the time of filing the JP patent application on which this patent application claims priority) in which arrangement an electron acceleration layer includes electric insulator particles and a basic dispersant; and an arrangement disclosed in Japanese Patent Application Publication Tokugan No. 2009-121454 (not yet laid open to the public at the time of filing the JP patent application on which this patent application claims priority) in which arrangement an electron acceleration layer includes just electric insulator particles.

The following describes a principle of electron emission. It is considered as follows: Crystal defect or surface treatment is carried out on a surface of an electric insulating material such as silica. This produces a part of the silica surface in which part electric resistance is low and thus electrons flow the part. The electrons on the part of the silica surface flow in a form of hopping conduction or the like, become hot electrons having high energy and then arrive at the thin-film electrode 9. It is considered, but not yet proven, that if the electrons have an energy not lower than a work function of a material (e. g., gold) constituting the thin-film electrode 9, the electrons are emitted out from the electron emitting element 4.

As described above, in the heating element radiator 1, the electrons emitted from the electron emitting element 4 into the atmosphere repeatedly collide with gas molecules at once, adhere mainly to molecular oxygen (electron attachment) at short times and then form negative ions of oxygen. In a case where an outer space of the electron emitting element 4 has an electric potential gradient to be more negative toward the electron emitting element 4 and more positive toward the heat sink 3, the negative ions of oxygen move to heat sink 3 along an electric field from the electron emitting element 4. The movement of the negative ions of oxygen is associated with collision of the negative ions of oxygen with neighboring neutral molecules (molecular nitrogen and molecular oxygen which are not electrically charged) present in the outer space. This causes the neutral molecules to move along the electric field. The movement of a mixture of the negative ions of oxygen and the neutral molecules along the electric field is an ionic wind. That is, in the heating element radiator 1, the electric potential gradient is formed in the outer space of the electron emitting element 4 (a positive voltage is applied to the heat sink 3 meanwhile a negative voltage is applied to the electron emitting element 4). This generates the ionic wind. The stronger the electric field is, the stronger the ionic wind becomes. Thus, a stronger electric field allows more effective heat exchange.

As such, the heating element radiator 1 does not generate a gas flow in vacuum. This increases a gas flow speed of the ionic wind, and in turn increases a cooling effect. In a case where the gas flow speed of the ionic wind is not sufficiently fast, the fan 23 shown in FIG. 2 can be used together.

The heat sink 3 of the heating element radiator 1 includes a concavity or a convexity, on at least a part of the heat sink 3. Such a concavity or a convexity included in the at least part of the heat sink allows heat to be transferred to a larger number of gas molecules. This increases a heat dissipation effect. The electron emitting element 4 is placed in parallel with the heat sink 3. This allows the ionic wind to arrive at the heat sink 3 while preventing concentration of the electric field in the electron emitting element. This in turn allows heated gas molecules to be removed entirely from a heat dissipation surface of the heat sink 3, and consequently increases the heat dissipation effect.

The voltage applied by the power supply 5 between the heat sink 3 and the thin-film electrode 9 of the electron emitting element 4 may be any voltage, provided that the voltage causes negatively charged ions to arrive at the heating element 2. The voltage preferably has a lower limit of higher than 0 V. For example, the lower limit is preferably +10 V or higher, more preferably +100 V or higher, or particularly preferably +200 V or higher. Further, the applied voltage may have any upper limit. Practically, in consideration of a limit (described below) on an electric field strength, the upper limit is preferably +10 kV or lower, or more preferably +1 kV or lower.

The electric field applied between the heat sink 3 and the thin-film electrode 9 of the electron emitting element 4 may have any strength. For example, the strength is 1 V/m or greater, preferably 10 V/m or greater, or more preferably 1000 V/m or greater. In order to prevent generation of ozone, the electric field strength has an upper limit of preferably 10⁷ V/m or lower, or more preferably 10⁶ V/m. This prevents generation of hazardous substances such as ozone and nitrogen oxides.

According to the present invention, it is preferable to connect the heat sink 3 to ground before the gas flow emitted from the electron emitting element 4 is blown toward the heat sink 3 which is in contact with the heating element 2. This prevents the heating element 2 from being charged up.

The gas flow generated by the electron emitting element 4 may be used in combination with an airflow generated by a rotary-blade airflow generator. Alternatively, such a rotary-blade airflow generator may not be used.

EXAMPLE 1

With reference to FIGS. 4 and 5, the following describes, as an example, experiments for verifying the heat dissipation effect achieved by the heating element radiator of the present embodiment. Note that these experiments merely serve as example embodiments, and that the description of the experiments does not limit the scope of the present invention.

The experiments of the present example were conducted with use of a heating element radiator illustrated in FIG. 4. The heating element radiator illustrated in FIG. 4 was equipped with a fan 14 thereby being configured to blow air toward the heat sink 3. The heating element 2 serving as a heat source was arranged to start or stop generating heat in response to an on-off action of a switch. When the switch was turned off, the heating element 2 would stop generating heat. In the present example, the heat generation by the heating element 2 was stopped (i.e., the switch was turned off) simultaneously with a start of temperature measurement with use of a temperature measuring terminal 15. The temperature measuring terminal 15 measured a surface temperature of the heat sink 3 without being in contact with the surface of the heat sink 3.

In the present example, after the heat generation by the heating element 2 was stopped, first and second experiments described below were conducted, in which experiments a temperature of the heating element 2 was measured over time. The heat dissipation effect was verified by making a comparison between the two experiments in terms of changes in the temperature of the heating element 2 over time.

In the first experiment, the heating element 2 was cooled only with use of air blown by the fan (airflow generator) 14, while the power supply 5 carries out no voltage application (i.e., no voltage was applied between the heat sink 3 and the electron emitting element 4). In the second experiment, the heating element 2 was cooled, while the power supply 5 generated an applied voltage, with use of a combination of (i) air blown by the fan 14 and (ii) ions 16 emitted from the electron emitting element 4.

The heating element radiator used in the first and second experiments was equipped with an air pipe 13 so that a gas flow rate was kept constant before and after the air blown by the fan 14 was mixed with a wind of ions 16. In the first and second experiments, the gas flow rate was 9 L/min. Further, in the second experiment, a current recovered at the heat sink 3 due to the electron emission caused by the voltage application was within a range from 10 μA to 14 μA.

FIG. 5 shows a result of measuring the temporal changes in the temperature of the heating element 2 in the first and second experiments. FIG. 5 shows that the temperature of the heating element 2 for the second experiment was lowered more rapidly than that of the heating element 2 for the first experiment. FIG. 5 further shows that, 60 seconds after the start of the temperature measurement, a temperature drop caused by the cooling of the second experiment was approximately 767% of a temperature drop caused by the cooling of the first experiment.

Second Embodiment

Another embodiment of the present invention is described below with reference to FIG. 6.

A heating element radiator of the present embodiment has a drive principle which is basically identical to that of the heating element radiator according to First Embodiment. Such an identical part of the drive principle is not described in this embodiment. The heating element radiator of the present embodiment differs from the heating element radiator of First Embodiment in that how the electron emitting element is arranged. FIG. 6 is a view illustrating the arrangement of the electron emitting element and its surroundings of the heating element radiator according to the present embodiment.

As illustrated in FIG. 6, an electron emitting element 16 is flexible. The electron emitting element 16 includes: a flexible substrate 17; a substrate thin-film electrode 18; the electron acceleration layer 8; and the thin-film electrode 9. The substrate thin-film electrode 18 and the thin-film electrode 9 are connected to the power supply 10. The electron emitting element 16 accelerates electrons between the substrate thin-film electrode 18 and the thin-film electrode 9 (i.e., in the electron acceleration layer 8) in response to a voltage applied between the substrate thin-film electrode 18 and the thin-film electrode 9. The electron emitting element 16 thus emits the electrons from the thin-film electrode 9.

Third Embodiment

Still another embodiment of the present invention is described below with reference to FIG. 7.

A heating element radiator of the present embodiment has a drive principle which is basically identical to that of the heating element radiator according to First Embodiment. Such an identical part of the drive principle is not described in this embodiment. The heating element radiator of the present embodiment differs from the heating element radiator of First Embodiment in that the electron emitting element is provided to a rotary-blade airflow generator. FIG. 7 is a view illustrating the rotary-blade airflow generator 19 included in the heating element radiator according to the present embodiment.

As illustrated in FIG. 7, the rotary-blade airflow generator 19 includes a blade 20, and is designed to rotate the blade 20 so as to blow air toward the heating element. The blade 20 is designed to be rotated along a rotation direction R (i.e., along a direction indicated by an arrow in FIG. 7) so as to blow air from a rear side toward a front side of the drawing (i.e., toward a viewer of the drawing). FIG. 7 indicates the air blow direction by S.

According to the heating element radiator of the present embodiment, the heat sink 3 is provided so as to face a surface 20 a of the blade 20 included in the rotary-blade airflow generator 19. The heat sink 3 is in contact with the heating element 2.

According to the heating element radiator of the present embodiment, the rotary-blade airflow generator 19 is provided with the electron emitting element 4 of First Embodiment or the electron emitting element 16 of Second Embodiment. In other words, the electrode substrate 7 or the flexible substrate 17 is placed on the surface 20 a of the blade 20.

This allows (i) the air from the rotary-blade airflow generator 19 and (ii) the charged gas (ions) from the electron emitting element 4 (or 16) to be simultaneously blown toward a conductive section which is attached to the heating element 2.

Fourth Embodiment

Yet another embodiment of the present invention is described below with reference to FIG. 8.

A heating element radiator of the present embodiment has a drive principle which is basically identical to that of the heating element radiator according to First Embodiment. Such an identical part of the drive principle is not described in this embodiment. The heating element radiator of the present embodiment differs from the heating element radiator of First Embodiment in that the electron emitting element takes a mesh structure. FIG. 8 is a view illustrating the electron emitting element included in the heating element radiator according to the present embodiment. FIG. 8 shows air is blown from a rear side toward a front side of FIG. 8 (i.e., toward a viewer of FIG. 8). FIG. 8 also indicates an air blow direction by S′.

As illustrated in FIG. 8, an electron emitting element 21 takes a mesh structure. The electron emitting element 21 includes a mesh substrate 22. The mesh substrate 22 has a plurality of openings 22 b which penetrate the mesh substrate 22 in the air blow direction S′. According to the heating element radiator of the present embodiment, the heat sink 3 is provided so as to face a surface 22 a of the mesh substrate 22. The heat sink 3 is in contact with the heating element 2. The air is thus blown along the air blow direction S′ through the openings 22 b toward the heat sink 3.

According to the heating element radiator of the present embodiment, the mesh substrate 22 is provided with the electron emitting element 4 of First Embodiment or the electron emitting element 16 of Second Embodiment. In other words, the electrode substrate 7 or the flexible substrate 17 is placed on the surface 22 a of the mesh substrate 22.

As described above, the heat exchanger of the present invention can stably blow an ionic wind even with a reduced interelectrode distance. This makes it possible to downsize a cooling device.

The electron emitting element serving as an electron source element can be formed by a coating method on a surface which is flexible or which has irregularities. This allows a TV set to include a cooling function in a cabinet section of the TV set. As a result, it is possible to simultaneously reduce the thickness of a liquid crystal display TV and cool a high-temperature portion of the TV.

In addition, since the reduced distance is accompanied with no electric discharge, no ozone or no nitrogen oxide is generated. Thus, the heat exchanger with such a reduced distance can be mounted in household electric appliances. For example, this configuration can increases the cooling effect of a refrigerant in a refrigerator, by improving spontaneous heat dissipation of the refrigerant. This allows for a reduction in power consumption and for downsizing of a compressor in the refrigerator. Further, as illustrated in FIG. 4, the heat exchanger can rapidly remove heat from the vicinity of a heat source. This advantage can be used to provide an ionic wind to a heat source of an air conditioner or a fan heater. This makes it possible to quickly serve warm air to a user. Moreover, since warm air can be provided efficiently, it is possible to reduce a heater output and consequently to reduce power consumption. Furthermore, in a case where the heat exchanger is included in a washer-dryer, the washer-dryer can also blow strong warm air toward wet clothes. It is therefore possible to reduce power consumption by reducing a heater output, and also to downsize the device (washer-dryer). In the case of the washer-dryer, the heat exchanger blows an ionic wind toward clothes. This prevents triboelectricity of the clothes thereby alleviating tangling of the clothes. As a result, it is possible to improve a drying efficiency and in turn to reduce a drying time.

Fifth Embodiment

The following describes further yet another embodiment of the present invention with reference to FIG. 9.

The electron emitting element and the air filter included in the heating element radiator of the present embodiment has arrangements identical to those of the electron emitting element and the air filter of First Embodiment. Such identical parts of the arrangements are not described in this embodiment. The heating element radiator of the present embodiment differs from the heating element radiator of First Embodiment in that the heating element radiator of the present embodiment includes a “heating element” serving as a “target of heat exchange”, exchanges heat between the heating element and air present along a surface of the heating element and directly cools the heating element by an ionic wind. That is, the heating element radiator of the present embodiment does not include a heat sink. FIG. 9 is a view schematically illustrating an arrangement of the heating element radiator of the present embodiment.

As illustrated in FIG. 9, the heating element radiator 1 is a device for releasing, to the outside, heat generated by a heating element 2′. The heating element radiator 1 includes: the electron emitting element 4; a power supply (second voltage applying means) 5′; and the power supply (first voltage applying means) 10 that applies a voltage between the electrode substrate 7 and the thin-film electrode 9 of the electron emitting element 4.

The electron emitting element 4 is separated from a surface 2 a′ of the heating element 2′ by a space, and thus provides electrons to the heating element 2′ via air in the space. The heating element 2′ and the electron emitting element 4 are connected to the power supply 5′. The power supply 5′ applies a voltage between the heating element 2′ and the electron emitting element 4. The voltage causes the electron emitting element 4 to emit electrons. These electrons collide with and adhere to air molecules present in the space between the heating element 2′ and the electron emitting element 4. The corrosion and adhesion then ionize the air molecules. The air molecules thus ionized move along an electric field generated between the heating element 2′ and the electron emitting element 4. This generates an ionic wind. The ionic ion brings ions thereof to the heating element 2′. This stirs and exchanges air molecules which are present along the surface of the heating element 2′. The arrival of the ions at the heating element 2′ will cause the heating element 2′ to be charged up. In order to prevent the heating element 2′ from being charged up, the heating element radiator 1 is connected to ground 6.

As described above, the heating element radiator includes the two power supplies 5 and 10. The power supply is used to accelerate electrons in the electron acceleration layer 8 of the electron emitting element 4 so that the electrons are emitted from the thin-film electrode 9. On the other hand, the power supply 5 is used to provide, to the heating element 2′, the electrons emitted from the thin-film electrode 9.

Further, the heating element radiator 1 includes: a fan 23 that serves as air supplying means which supplies an airflow to the space between the heating element 2′ and the electron emitting element 4; and an air filter 24. The air filter 24 is provided between (i) the space between the heating element 2′ and the electron emitting element 4 and) the fan 24. Airflow 23 a supplied by the fan 23 flows, via the air filter 24, into the space between the heating element 2′ and the electron emitting element 4.

As described above, in the heating element radiator 1, the airflow 23 a flows, via the air filter 24, into the space between the heat sink 3 and the electron emitting element 4. This allows the airflow 23 a from which dust is removed to flow to a surface of the thin-film electrode 9. The heating element radiator 1 therefore can prevent adhesion of dust and traces of gas to the surface of the thin-film electrode 9.

(Use of Heat Exchanger of The Present Invention as Heating Device)

The principle of generating an ionic wind described in the foregoing Embodiments is applicable to a heating device. The following describes use of the heat exchanger of the present invention as a heating device.

In a case where the heat exchanger of the present invention is used as the heating device, examples of an arrangement of the heating device include: an arrangement (i) in which hot air is effectively generated so as to heat a low-temperature object; and an arrangement (ii) in which a low-temperature conductive solid is heated by high-temperature air.

In a case of the arrangement (i) in which hot air is effectively generated so as to heat a low-temperature object, it is possible to normally transfer high-temperature air generated by effective heat exchange to the low-temperature object so as to heat the low-temperature object, by use of an arrangement completely identical to that of the above-described heating element radiator 1. That is, the above-described heating element radiator 1 exchanges heat between a target of heat exchange (the heat sink 3 or the heating element 2) and the air present along the surface of the target of heat exchange. This cools the target of heat exchange. At the same time, heat is emitted from the surface of the target of heat exchange. This heat causes the air between the target of heat exchange and the electron emitting element 4 to reach a high temperature. The arrangement (i) is an arrangement in which the low-temperature object is heated by use of the high-temperature air between the target of heat exchange and the electron emitting element 4 The heating device having such an arrangement is used for, for example, a fan heater that effectively generates warm air.

In a case of the arrangement (ii) in which a low-temperature conductive solid (target of heat exchange) is heated by high-temperature air, the arrangement (ii) is applicable to, for example, a system in which high-temperature gas that generates in an incinerator which high-temperature gas becomes waste heat is used, as a heat source, for heating. If the electron emitting element and the target of heat exchange that has electrical conductivity are simultaneously used with the system, it is possible to attain a greatly effective waste heat recovery heating system.

The present invention is not limited to the description of the embodiments above, but may be altered by a skilled person within the scope of the claims. An embodiment based on a proper combination of technical means disclosed in different embodiments is encompassed in the technical scope of the present invention.

As described above, the electron emitting element included in the heat exchanger of the present invention including: an electrode substrate; a thin-film electrode; first voltage applying means for applying a voltage between the electrode substrate and the thin-film electrode; and an electron acceleration layer which accelerates electrons inside the electron acceleration layer in response to the voltage applied by the first voltage applying means so that the electrons thus accelerated are emitted from the thin-film electrode, the electron acceleration layer being made at least partially of an electric insulating material, the heat exchanger including: an air filter through which air flows onto a surface of the thin-film electrode.

It is preferable to arrange the heat exchanger of the present invention such that the air filter is a filter that collects and filters dust. This can reliably prevent adhesion of dust to the surface of the electron emitting element.

The air filter included in the heat exchanger of the present invention may be a filter that collects and filters traces of gas in an atmosphere. The “traces of gas in an atmosphere” described here is VOC (volatile organic compounds), ozone, vapor or the like. VOC has volatility and is a general term of an organic compound that becomes a gas in the atmosphere. Examples of VOC include various substances such as toluene, xylene and ethyl acetate. As described above, the air filter 24 is a filter that collects and filters traces of gas in the atmosphere. This reduces adhesion of traces of gas to the electron emitting element and therefore yields an effect of preventing deterioration in a capability of the electron emitting element which deterioration is caused by the adhesion of traces of gas to the electron emitting element: Further, as described above, in order to collect and filter traces of gas in the atmosphere, the air filter 24 preferably includes at least one of active carbon, manganese dioxide and titanium oxide. The active carbon absorbs various traces of gas, the manganese dioxide is advantageous mainly to resolution of ozone, and the titanium oxide is advantageous to resolution of VOC.

It is preferable to arrange the heat exchanger of the present invention such that the electric insulating material constituting the at least part of the electron acceleration layer includes particulate electric insulating particles.

According to the arrangement, the electric insulating material constituting the at least part of the electron acceleration layer includes the particulate electric insulating particles. It is therefore possible to easily adjust a resistance value of the electron acceleration layer.

It is preferable to arrange the heat exchanger of the present invention such that the electric insulating material constituting the at least part of the electron acceleration layer includes either at least one of SiO₂, Al₂O₃ and TiO₂, or an organic polymer.

According to the arrangement, the electric insulating material includes either at least one of SiO₂, Al₂O₃ and TiO₂, or an organic polymer. These materials have a high insulating property. It is therefore possible to adjust the resistance value of the electron acceleration layer so as to fall in a desired range.

It is preferable to arrange the heat exchanger of the present invention such that the thin-film electrode includes at least one of gold, carbon, nickel, titanium, tungsten and aluminum.

As described above, the thin-film electrode includes at least one of gold, carbon, nickel, titanium, tungsten and aluminum. These materials have a low work function. This allows the electrons accelerated in a particle layer to effectively tunnel. It is thus possible to emit more electrons having a high energy outside the electron emitting element.

It is preferable to arrange the heat exchanger of the present invention such that the electric insulating particles each have an average diameter which falls within a range from 10 nm to 1000 nm. In this case, a dispersion state of a particle diameter may be broad with respect to the average diameter. For example, in a case where a particle has 50 nm of average diameter, the particle diameter may range from 20 nm to 100 nm.

According to the arrangement, the electric insulating particles each have an average diameter which falls within a range from 10 nm to 1000 nm. This allows effective heat conduction from inside to outside of electrically conductive particles smaller in size than the electric insulating material and therefore effectively releases Joule heat that generates at the time of the passage of an electric current within the electron emitting element. It is therefore possible to prevent the electron emitting element from being destroyed by the Joule heat. This also allows easy adjustment of the resistance value of the electron acceleration layer.

The heat exchanger may be a cooling device for cooling a heating element that serves as the target of heat exchange.

The target of heat exchange included in the heat exchanger of the present invention may be a heat sink having an up-and-down surface which faces the electron emitting element. The heat sink contacts with an object that is subject to heat exchange in the heat exchanger so as to exchange heat with the object that is subject to heat exchange. This can improve a heat exchange effect.

It is preferable to arrange the heat exchanger of the present invention such that the electron emitting element is configured to generate a gas flow in an atmosphere.

According to the arrangement, the electron emitting element is configured to generate a gas flow in the atmosphere. This increases an airflow speed of an ionic wind and therefore increases the heat exchange effect.

It is preferable that the heat exchanger of the present invention includes a fan which provides an airflow to a surface of the thin-film electrode.

The arrangement can increase the heat exchange effect even in a case where the airflow speed of the ionic wind is not sufficiently fast (in a case where an electric field of the outer space is weak and therefore the ionic wind is weak).

It is preferable that the heat exchanger of the present invention includes a rotary-blade airflow generator which includes blades provided so as to face the target of heat exchange and which rotates the blades so as to blow air toward the target of heat exchange, wherein the electron emitting element is provided on a surface of at least one of the blades, the surface being opposite to the target of heat exchange.

According to the arrangement, the electron emitting element is provided on the surface of the at least one of the blades of the rotary-blade airflow generator, the surface being opposite to the target of heat exchange. This allows ions generated by collision of electrons that are emitted from the electron emitting element to arrive at the target of heat exchange on air blown toward the target of heat exchange. That is, the ions arrive at the target of heat exchange in a state of no resistance against an airflow. As a result, the arrangement not only can increase a wind power and therefore can increase the heat exchange effect due to a charged airflow but also can attain reduction of the heat exchanger in size and reduction in power consumption.

It is preferable to arrange the heat exchanger of the present invention such that the electron emitting element has a mash structure.

The arrangement makes it easy to suck air from a backside of the electrode substrate thereby easily transferring the air to a contact member from a whole surface of the electron emitting element. This increases air volume and therefore increases the heat exchange effect.

It is preferable that the heat exchanger of the present invention includes second voltage applying means for applying a voltage between the target of heat exchange and the electron emitting element, wherein the voltage applied by the second voltage applying means is higher than 0 V but is not higher than +10 kV.

According to the arrangement, the heat exchanger of the present invention includes the second voltage applying means for applying the voltage between the target of heat exchange and the electron emitting element, wherein the voltage applied by the second voltage applying means is higher than 0 V but is not higher than +10 kV. That is, the voltage applied by the second voltage applying means is higher than the voltage applied by the first voltage applying means. The arrangement thus allows negatively charged ions to arrive at the target of heat exchange. It is therefore possible to release heat of the target of heat exchange.

It is preferable to arrange the heat exchanger of the present invention such that a strength of an electric field generated between the target of heat exchange and the electron emitting element falls within a range from 1 V/m to 10 ⁷ V/m.

The arrangement makes it possible to provide electrons to molecular oxygen present in the air molecules with use of energy lower than 6 eV that is dissociation energy of oxygen. It is therefore possible to prevent occurrence of harmful substances such as ozone and nitrogen oxide. That is, energy of the electrons becomes 1 eV before the electrons collide with the air molecules in a case where the strength of the electric field is 10⁷ V/m because mean free path of an electron in the atmosphere is 0.1 μm. It is therefore possible to prevent production of ozone and nitrogen oxide by setting the electric field to be lower than 10⁷ V/m.

It is preferable to arrange the heat exchanger of the present invention such that the target of heat exchange is grounded.

This can prevent the target of heat exchange from being charged up.

It is preferable to arrange the heat exchanger of the present invention such that the target of heat exchange is separated from the electron emitting element by a distance which falls within a range from 100 μm to 50 cm.

This makes it possible to bring the target of heat exchange close to the electron emitting element and therefore to increase the heat exchange effect. Further, the electron emitting element is configured with a material that is difficult to oxidize. This can drive the electron emitting element for long periods even in the vicinity of a high-temperature material.

INDUSTRIAL APPLICABILITY

The heat exchanger of the present invention can stably blow an ionic wind even with a reduced interelectrode distance. This allows for downsizing of a cooling device. The heat exchanger of the present invention is applicable to liquid crystal display TVs and laptop personal computers, both of which require efficient cooling within a small space and prevention of wind noise caused by a fan.

REFERENCE SIGNS LIST

-   1: heating element radiator (heat exchanger, cooling device) -   2: heating element -   2′: heating element -   3: heat sink (target of heat exchange)

04: electron emitting element

-   5: power supply (second voltage applying means) -   5′: power supply (second voltage applying means) -   6: ground -   7: electrode substrate -   8: electron acceleration layer -   9: thin-film electrode -   10: power supply (first voltage applying means) -   11: electric insulator particle (electric insulating material) -   12: metal particle (electrically conductive particle) -   13: air pipe -   14: fan -   15: temperature measuring terminal -   16: ion -   17: flexible substrate -   18: thin-film electrode -   19: rotary-blade airflow generator -   20: blade -   20 a: surface -   21: electron emitting element -   22: mesh substrate -   22 a: surface -   23: fan (fan that supplies airflow to surface of thin-film     electrode) -   24: air filter 

1. A heat exchanger, comprising: an electron emitting element; and an air filter, the electron emitting element being provided so as to be separated, by a space, from a target of heat exchange having electrical conductivity and providing electrons to the target of heat exchange via air in the space, and the heat exchanger exchanging heat between the target of heat exchange and the air, the electron emitting element including: an electrode substrate; a thin-film electrode; first voltage applying means for applying a voltage between the electrode substrate and the thin-film electrode; and an electron acceleration layer which accelerates electrons inside the electron acceleration layer in response to the voltage applied by the first voltage applying means so that the electrons thus accelerated are emitted from the thin-film electrode, the electron acceleration layer being made at least partially of an electric insulating material, and the air filter filtering air to flow onto a surface of the electron emitting element.
 2. The heat exchanger as set forth in claim 1, wherein: the air filter is a filter that collects and filters dust.
 3. The heat exchanger as set forth in claim 1, wherein: the air filter is a filter that collects and filters traces of gas in an atmosphere.
 4. The heat exchanger as set forth in claim 3, wherein: the air filter includes at least one of active carbon, manganese dioxide and titanium oxide.
 5. The heat exchanger as set forth in claim 1, wherein: the electric insulating material constituting the at least part of the electron acceleration layer includes particulate electric insulating particles.
 6. The heat exchanger as set forth in claim 1, wherein: the electric insulating material constituting the at least part of the electron acceleration layer includes either at least one of SiO₂, Al₂O₃, and TiO₂, or an organic polymer.
 7. The heat exchanger as set forth in claim 1, wherein: the thin-film electrode includes at least one of gold, carbon, nickel, titanium, tungsten and aluminum.
 8. The heat exchanger as set forth in claim 5, wherein: the electric insulating particles each have an average diameter which falls within a range from 10 nm to 1000 nm.
 9. The heat exchanger as set forth in claim 1, being a cooling device for cooling a heating element that serves as the target of heat exchange.
 10. The heat exchanger as set forth in claim 1, wherein: the target of heat exchange is a heat sink having an up-and-down surface which faces the electron emitting element.
 11. The heat exchanger as set forth in claim 1, wherein: the electron emitting element is configured to generate a gas flow in an atmosphere.
 12. The heat exchanger as set forth in claim 1, comprising: a fan which provides an airflow to a surface of the thin-film electrode.
 13. The heat exchange as set forth in claim 1, comprising: a rotary-blade airflow generator which includes blades provided so as to face the target of heat exchange and which rotates the blades so as to blow air toward the target of heat exchange, wherein the electron emitting element is provided on a surface of at least one of the blades, the surface being opposite to the target of heat exchange.
 14. The heat exchanger as set forth in claim 1, wherein: the electron emitting element has a mash structure.
 15. The heat exchanger as set forth in claim 1, comprising: second voltage applying means for applying a voltage between the target of heat exchange and the electron emitting element, wherein the voltage applied by the second voltage applying means is higher than 0 V but is not higher than +10 kV.
 16. The heat exchanger as set forth in claim 15, wherein: a strength of an electric field generated between the target of heat exchange and the electron emitting element falls within a range from 1 V/m to 10⁷ V/m.
 17. The heat exchanger as set forth in claim 1, wherein: the target of heat exchange is grounded.
 18. The heat exchanger as set forth in claim 1, wherein: the target of heat exchange is separated from the electron emitting element by a distance which falls within a range from 100 μm to 50 cm. 